The invention relates generally to earth moving buckets and more specifically to backhoe buckets having a plurality of teeth disposed in a symmetrical arrangement along upwardly and rearwardly inclined bucket edges.
The backhoe is the mainstay of modern earth excavating and trenching equipment. A modern backhoe typically includes two boom structures which are pivotally interconnected. One of the booms may, optionally, be extensible. Pivotally secured to the free end of one of the booms is a pivotable bucket and the entire assembly is pivotally secured to a support which typically may be rotated about a vertical axis in a semi-circle. Suitably arranged and controlled double acting hydraulic cylinders provide motive force to these components.
The backhoe is a hybrid device which combines several features from prior art devices such as the shovel style and the drag line bucket excavators. The shovel style bucket excavator includes a shovel bucket disposed on a movable boom which includes teeth along the forward lower marginal edge. The bucket thus cuts and excavates while moving upwardly and/or away from the machine. The reaction forces to such movement tend to lift the rear portion of the machine. In the prior art, this problem was generally overcome by, first of all, building large, heavy machines and, second of all, adding additional weight to the rear portion thereof to counterbalance the digging forces. All of these approaches resulted in equipment which was costly, difficult to transport from job site to job site and was inefficient in operation. Since the bucket was, however, directly mounted upon a rigid boom, the digging accuracy thereof was good.
The drag line bucket is suspended from a single boom by a plurality of cables which typically may be independently played in or out to control the movement of the buckets. The cutting and excavating process is, of course, achieved while the bucket is being drawn toward the body of the machine and thus, due to the typically good frictional engagement between the machine and the ground, the maintenance of the machine in a stationary position during the excavation operation is not a problem. Accuracy, however, is. Harmonic oscillation of the bucket as it is being placed in position to continue a cut after it has been emptied is difficult to control. The drag line bucket therefore has been typically relegated to larger scale excavating operations wherein precise cuts and narrow trenches, for example, are not required.
The modern backhoe, as noted above, utilizes a pair of pivotally interconnected booms similar to those utilized in a shovel style excavator to provide accuracy of cut. The multiple axis movement of the bucket on the backhoe boom also permits cutting and excavating while the bucket is moving toward the backhoe, in the manner of the drag line bucket, thus eliminating reaction forces which may tend to raise the backhoe from the ground. The backhoe, it should also be appreciated, is capable of exceptionally accurate excavation.
Because of these advantages, the backhoe has been called upon to perform digging, excavating and trenching operations in increasingly difficult situations. For example, such excavating devices are frequently called upon to dig in hard materials such as frozen ground, broken concrete, and hard rock formations such as caliche, limestone and soapstone.
In such situations, several options have been available in the prior art. A common approach is to utilize a pick point on the backhoe to break up the hard material. Under certain circumstances such as digging through frozen ground to below the frost line, this expedient may be readily utilized inasmuch as only a relatively thin layer of hard material may need to be fractured before regular digging may be resumed with a conventional backhoe bucket. Obviously, the greater the relative quantity of hard material that must be fractured with the pick, the longer the excavating or trenching operation may take. To excavate a trench through caliche in this manner may thus substantially double the length of time required to complete the trench. For a contractor who did not anticipate such difficulties, the additional machine and personnel time will be costly.
A second approach may be to simply utilize conventional backhoe buckets and equipment in order to dig primarily by brute force. While this method will meet with varying success depending upon the particular material encountered, the deleterious effect upon equipment subjected to such service and perhaps the outright damage thereof militates against it. U.S. Pat. No. 3,065,557 discloses a third alternative wherein an impact hammer mechanism is disposed within a backhoe bucket itself and is utilized to penetrate and fracture various hard materials. Unfortunately this bucket design necessitates the supply of hydraulic fluid to the backhoe bucket. Such a system appears to be somewhat complicated and thus prone to service related failure.